Which case, and why?

Chapter on the explanation of expressions current among this group, and the clarification of what is obscure in them. Know that it is well established that every group of scholars has expressions which they use, which they hold exclusively, apart from everyone else, and on which they have agreed among themselves for purposes of their own: to bring the meaning closer to the understanding of those addressed by them, or to make it easier for the practitioners of that discipline to grasp their meanings when the expressions are used without qualification. This group, too, employs expressions among themselves by which they intend to disclose their meanings to one another, while keeping them concise and veiled from those who differ from them in their way, so that the meanings of their expressions remain obscure to outsiders. They do this out of jealous protectiveness over their secrets, lest these spread among those not fit for them. For their realities are not gathered by any kind of contrived effort, nor obtained by any manner of personal contrivance. Rather, they are meanings which God, exalted is He, has deposited in the hearts of a certain folk, and for whose realities He has singled out the innermost secrets of a certain folk. We wish to explain these expressions to make understanding easier for those who wish to grasp their meanings, from among those who travel their paths and follow their customs.